import  random
num1= random.randint(65, 122)
num2= random.randint(65, 122)
num3= random.randint(65, 122)
num4= random.randint(65, 122)
num=[num1,num2,num3,num4]
def check_num(num):
    if((num1<97)and(num1>90) or (num2<97)and(num2>90) or (num3<97)and(num3>90) or (num4<97)and(num4>90)):
        return False
    else:
        return True

while(check_num(num)):
    print("输入的四个随机字母为：{}，{}，{}，{}".format(chr(num1),chr(num2),chr(num3),chr(num4)))
    break